The present invention relates to the art of fuel flow control devices, and more particularly to a fuel flow control system for controlling fuel flow from a fuel source to the fuel rail of a fuel injected internal combustion engine.
In the trucking industry, a substantial portion of the overhead is attributable to the cost of the fuel consumed by the trucks. Anything which can reduce fuel costs and thereby lower the operating overhead of the business would be welcomed. Because of this, engine control systems have been devised which prevent excessive fuel consumption by limiting the maximum speed of the trucks.
One known manner of limiting the maximum speed of trucks is by blocking fuel flow to the engine of the truck whenever the vehicle speed exceeds acceptable limits. The patent to Ruhl, U.S. Pat. No. 4,245,598 discloses a system typifying this approach. In this patent the fuel limitation is accomplished by means of a solenoid valve connected between the fuel rail of the diesel engine and the fuel tank. When open, the valve permits fuel flow to bypass the engine, thereby reducing fuel flow to the engine. The valve is normally closed and only opens when the truck speed exceeds acceptable limits. Another prior system, manufactured and sold by Hewitt Industries of Los Angeles, Calif., accomplished the fuel limitation through use of a solenoid valve actually connected in series between the fuel pump and the fuel rail of the engine. Here, the valve was normally open and was only closed when the speed exceeded the desired limit.
The patents to Van Dine, U.S. Pat. No. 4,183,334 and Sumiyoshi, U.S. Pat. No. 4,207,849 disclose systems wherein fuel flow to a carburated internal combustion engine is modulated incrementally by actuating selected ones of plural on-off solenoid valves which are connected in parallel fuel flow paths. In these systems the smallest increment by which fuel flow can be varied is dependent upon the number of valves used. A large number of parallel valves is required if fine fuel flow control over a broad range of flow rates were desired.
The patent to Cromas et al., U.S. Pat. No. 4,203,395 discloses a closed loop idle speed control for a fuel injected engine wherein pulse width modulated valves are used to control the amount of air which bypasses the throttle valve in the engine so as to maintain a smooth idle speed. The pulse width modulated solenoid valve is used to supply operating fluid to a single-acting mechanical actuator controlling the bypass of air. In the patents to Aono, U.S. Pat. Nos. 4,046,118, 4,057,042, and 4,103,695 a pulse width modulated valve is used to directly control the supply of fuel to the fuel wells of a carburated internal combustion engine. By pulse width modulating the valve, proportional fluid flow control is provided through use of only a single valve. Unfortunately, fluid flow control at the lower end of the fluid flow control range is rather coarse since the duty cycle of the pulse width modulated signal is then quite small.